Question 1

How do I calculate tons of asphalt for a full-depth pavement section?

Accepted Answer

Use the AASHTO formula: tons = Area(sqft) × Depth(ft) × 145 lbs/ft³ ÷ 2000. Calculate base and surface courses separately and sum them. Multiply by the compaction factor (typically 1.10–1.15) to get loose tons for ordering. For example, 2000 sqft with 4 in base and 2 in surface at factor 1.10 = (2000 × 0.333 × 145 ÷ 2000 + 2000 × 0.167 × 145 ÷ 2000) × 1.10 ≈ 53.6 loose tons.

Question 2

What is a compaction factor in asphalt paving and why does it matter?

Accepted Answer

The compaction factor is the ratio of loose asphalt weight to its final compacted weight. Dense-grade HMA typically has a factor of 1.10–1.15, meaning you order 10–15% more loose tons than the compacted design quantity. Asphalt plants always bill by loose tons, so using the wrong factor will leave you under-ordered. Confirm the factor with your Job Mix Formula (JMF).

Question 3

How much tack coat do I need per square yard?

Accepted Answer

AASHTO M 208 specifies 0.05–0.15 gal/sqyd of emulsified tack coat (SS-1h or CRS-2). Use the lower end (0.05–0.08 gal/sqyd) for clean, new pavement surfaces and the higher end (0.10–0.15) for dry, aged, or porous surfaces. Over-application creates a slip plane; under-application causes delamination. Apply in a uniform spray pattern and allow to cure until brown turns to black (15–30 min) before placing overlay.

Question 4

What is RAP in asphalt and how does it save money?

Accepted Answer

RAP (Reclaimed Asphalt Pavement) is recycled asphalt milled from existing road surfaces. It contains both aggregate and aged binder that can replace virgin material in new mixes. RAP typically costs 20–40% of virgin asphalt, so even a 25% RAP substitution produces significant savings. FHWA allows up to 25% RAP without special binder adjustment; higher percentages require a softer virgin binder to compensate for aged RAP binder stiffness.

Question 5

What is the AASHTO pavement thickness for different traffic levels?

Accepted Answer

AASHTO Pavement Design Guide recommends: Very Light (<100 AADT): 3.5 in total (2 in base + 1.5 in surface); Light (100–1,000 AADT): 3.5–5 in; Medium (1,000–5,000 AADT): 5–6 in; Heavy (5,000–20,000 AADT): 6–9 in; Very Heavy (>20,000 AADT): 9–11 in, requiring full AASHTO design by a licensed pavement engineer.

Question 6

Why do asphalt plants bill by loose tons, not compacted tons?

Accepted Answer

Asphalt plants weigh the mix as it loads into trucks — before it is compacted into the pavement. This loose weight is the only quantity they can accurately measure. The compacted weight in the ground is always less, depending on the mix type and rolling effort. Contractors must convert their design (compacted) quantities to loose tons using the compaction factor before placing orders.

Question 7

How many truck loads of asphalt do I need?

Accepted Answer

A standard end-dump or transfer truck carries 10–15 tons of hot mix asphalt, with 12 tons per load being the most common planning figure. Divide your total loose tons by 12 to estimate truck loads. For large projects, stagger truck arrivals 10–15 minutes apart to keep the paver moving without backup — trucks waiting too long cause the mix to cool below its compaction temperature window (275°F / 135°C).

Question 8

What is the difference between base course and surface course asphalt?

Accepted Answer

The base course (binder course) uses a coarser aggregate mix designed for structural load distribution. It is typically 2–6 inches thick. The surface course (wearing course) uses a finer aggregate and polymer-modified binder for wear resistance, waterproofing, and skid resistance. It is typically 1.5–3 inches thick. For AASHTO full-depth design, both are required and calculated separately because they may use different mix types and densities.

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